1. Field of the Invention
The present invention relates to a ground impregnating process comprising injecting an alkaline ground impregnating material such as sodium silicate-based consolidating medium (sodium silicate is also referred to as "water glass"), with carbon dioxide gas joining the impregnating material, into a ground such as a weak ground or a water-leaked ground to provide consolidation or water cut-off of the ground, and particularly, to such a process, wherein control of the absolute flow rate of pressurized carbon dioxide gas is simplified, and carbon dioxide gas is allowed to join the aqueous sodium silicate solution at a given ratio to the aqueous sodium silicate solution within a range of acceptable ground pressures.
2. Description of the Prior Art
There has been proposed a medium injection process for injecting a medium consisting of an alkaline ground impregnating material such as sodium silicate and carbon dioxide gas serving as a hardening agent into a weak or water-leaked ground to provide consolidation or water cut-off of the ground.
In general, in injecting an aqueous sodium silicate solution and carbon dioxide gas into a ground in a joining manner, uniform aggregates of sodium silicate will be not formed unless carbon dioxide gas to be mixed is supplied at a substantially constant proportion in absolute quantity to the aqueous sodium silicate solution. This reason is as follows: If the pressure within the ground varies, the amount of carbon dioxide gas injected substantially varies, resulting in a failure to maintain a constant ratio to the sodium silicate, causing non-uniformity of a colloid material produced from the reaction of the sodium silicate and carbon dioxide and thus, a uniform aggregate is not provided. For example, in injection into the ground, if an injection rate per minute is kept constant, the injection pressure varies normally from zero to about 20 kg/cm.sup.2. On the contrary, because the aqueous sodium silicate is liquid, the absolute amount thereof would not vary even if the injection pressure varies. However, carbon dioxide varies in volume and also in absolute amount if the injection pressure varies.
For one of approaches to the above problems, there has been proposed a medium injection system as described in Japenese Patent Publication No. 42769/84. This proposed system comprises an injection pipe inserted into a ground, a sodium silicate storage tank connected to the interior of the injection pipe, and a carbon dioxide gas bomb, wherein a pressure variation senser is interposed between the carbon dioxide bomb and the injection pipe, the pressure variation sensor being constituted of an automatic flow rate adjuster valve, a flow meter connected via a differential pressure transmitter and an opening and closing operator to a flow rate indication adjuster, and a pressure transmitting unit similarly connected via a graphic operator to the flow rate indication adjuster, these three components being connected sequentially between the injection pipe and the carbon dioxide tank, so that the absolute flow rate of carbon dioxide gas is controlled by the automatic flow rate adjuster valve operated by the flow rate indication adjuster on the basis of the results of calculation in both the operators, thereby injecting the aqueous sodium silicate solution and the carbon dioxide gas in a joining manner at a constant ratio of their absolute flow rates.
The above prior art injection system can provide an advantage that the provision of the pressure variation sensor between the carbon dioxide tank and the injection pipe makes it possible to inject the aqueous sodium silicate solution and carbon dioxide gas into a ground in a joining manner at a constant ratio of their aboslute flow rates, irrespective of a variation in ground pressure (kg/cm.sup.2). In practice with this system, however, there is a necessity for a complicated control system for sensing a variation in ground pressure to supply a pressurized carbon dioxide gas in an amount to correspond to the ground pressure, resulting in an increased cost of equipment for the control system, and also providing practical problems of requirements for check in performance, control and maintenance of individual control elements as well as careful control of operation.